The present invention relates to polarized signal receiver waveguides in general, or so-called "feedhorns", as used in dish antennas for TVRO (televisions receive only) systems, and more particularly to a novel receiver probe for signal receiving and signal transmitting waveguides.
The RF signals transmitted by communication satellite transponders consist of two linearly polarized signals, rotated 90.degree. from each other. The linearly polarized signals reflected by the dish are received through the open end of a feedhorn, installed at the focus of the dish and comprising a cylindrical waveguide of circular cross-section. Only one of the two polarized signals is received, the other signal being reflected out of the feedhorn. The detected signal is fed through a second waveguide, generally a waveguide having a rectangular cross-section, whose axis is conventionally disposed at 90.degree. to the axis of the feedhorn waveguide, and which feeds the detected signal to a low-noise amplifier (LNA).
Various antenna probe arrangements may be used for receiving one of the polarized signals in the feedhorn circular waveguide and for launching, or re-transmitting the detected signal into the rectangular waveguide. Generally, the antenna probe comprises a receiver portion disposed in the circular waveguide, and a signal launch or re-transmitter portion disposed in the rectangular waveguide, the probe being supported by a rotatable dielectric rod driven by a servomotor mounted on the waveguide assembly. The launch or re-transmitter portion of the probe has its axis aligned with the axis of the circular waveguide and with the axis of the dielectric rod, such as to remain constantly perpendicular to the axis of the rectangular waveguide during rotation of the probe. The probe receiver portion has its longitudinal axis perpendicular to the axis of rotation such as to rotate between the two orthogonally polarized signals in the circular waveguide. By rotation to a desired position, one polarized signal is received and the other is reflected. The received signal is conducted by the transmission line portion of the probe through the rear wall of the circular waveguide and is launched or re-transmitted into the rectangular waveguide by the probe launch or re-transmitter portion.
As the waveguide assembly is installed in an outdoor TVRO dish antenna, the assembly is exposed to inclement weather, such as rain or snow, dust and high wind, and to atmospheric pollution, all adverse conditions that may cause rapid deterioration, corrosion of the metallic surfaces and loosening of the joint between the waveguides. There results further deterioration of the relatively low level ultra-high frequency signals captured by the antenna system.
The invention disclosed in U.S. Pat. No. 4,554,553 is an improvement upon the prior art polarized signal receiver, transmission and launch probes for receiving a selected one of linearly polarized electromagnetic signals in one waveguide and for launching the selected signal into a second waveguide, the axes of the waveguides being disposed at right angle. The probe comprises a signal receiver portion disposed in a plane perpendicular to the axis of the first waveguide and a launch or re-transmitting portion having its axis perpendicular to the axis of the second waveguide. The probe launch portion is mounted in a controllably rotatable dielectric rod, such that rotation of the rod causes rotation of the signal receiver portion for alignment with a selected one of the polarized signals. The transmission line between the signal receiver probe portion and the signal launch probe portion consists of a pair of bifurcated branches forming a rectangle disposed along the axis of the first waveguide.
The invention disclosed in co-pending application Ser. No. 820,721 provides a single-piece waveguide assembly having a hemispherical concave rear end wall for a circularly cylindrical waveguide, and a rotatable probe provided with a transmission line between the receiver portion of the probe and the launching or re-transmitting portion of the probe which is contoured to the hemispherical shape of the wall.